Systematic errors in the light curves are corrected in the Presearch Data Conditioning (PDC) Pipeline component with basis vectors derived from the ensemble behavior of quiet targets and a Bayesian Maximum A Posteriori (MAP) approach to cotrending [1]}, [2]}, [3]}, [4]}. Compensation for crowding in the photometric aperture and for the fraction of target flux that is not captured in the photometric aperture is also performed in PDC; these adjustments to the flux values are based on quarterly crowding and flux fraction estimates [5]}, [6]}. The CAL, PA, and PDC components represent the front end of the Kepler Pipeline. The computational unit of work for these components is one CCD readout channel for one observing quarter.Each of the 42 CCD detectors on the focal plane assembly is divided into two independent readout channels for a total of 84 channels; two of the CCD detectors representing four readout channels failed in Q4 as described earlier.
